Extended O-GlcNAc on HLA Class-I-Bound Peptides

Area of Science:

• Immunology
• Glycobiology
• Mass Spectrometry

Background:

• Human leukocyte antigen (HLA) class I molecules present peptides to T cells, crucial for immune surveillance.
• Glycosylation, the addition of sugars, typically occurs on proteins in the endoplasmic reticulum and Golgi apparatus.
• O-linked glycosylation is a common post-translational modification, but its role on HLA-bound peptides is not well understood.

Purpose of the Study:

• To investigate unexpected mass spectrometric observations of glycosylated HLA class I-bound peptides.
• To characterize the nature and origin of these glycosylations.
• To explore the potential immunogenicity of these modified peptides.

Main Methods:

• Mass spectrometry for peptide and glycan analysis.
• Molecular modeling to understand structural implications.
• In vitro enzymatic assays to confirm glycosyltransferase activity.
• Oxonium ion pattern analysis for glycan structure elucidation.

Main Results:

• Identification of O-linked glycans on HLA class I peptides, extending beyond typical terminal modifications.
• Proposal that these glycans are extended O-N-acetylglucosamine (O-GlcNAc) structures, not GalNAc-initiated.
• First report of natural HLA class I presentation of O- and N-linked glycopeptides derived from membrane proteins.
• Observed that centrally located oligosaccharides on HLA class I peptides can be immunogenic.

Conclusions:

• HLA class I peptides can undergo complex O-GlcNAc glycosylation due to their trafficking through glycosylation-competent cellular compartments.
• These glycosylated HLA peptides, particularly those with central oligosaccharides, represent potential targets for immune surveillance.
• This finding expands the understanding of post-translational modifications on HLA molecules and their implications for immunity.